Drum for fixing sheet-type member

ABSTRACT

A printing plate is only guided by and wound around peripheral surfaces of cylinders. The cylinders are disposed along an axis of a rotating shaft at predetermined intervals, and support the entire printing plate with substantially equal balance. The printing plate has a degree of firmness, and thus, the printing plate can hold itself in a substantially cylindrical shape even if it is merely rolled in the air. Therefore, the whole printing plate can be accurately wound and held onto a peripheral locus of a predetermined radius coaxial with the rotating shaft merely by disposing guide members as auxiliary guides for positioning and winding parts of the printing plate.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a drum (rotating body) for disposing asheet-type member on a circumferential locus of a predetermined radiuscentering around a rotation axis.

2. Description of the Related Art

Conventionally, some image exposure apparatuses, which subject printingplates to image exposure, wind a printing plate onto a rotating drum andirradiate the printing plate with a light beam in accordance with imagedata while rotating the printing plate integrally with the rotatingdrum, so as to scan-expose the printing plate.

When the printing plate is wound onto the rotating drum, the printingplate is fixed onto the rotating drum by chucks so that both edges ofthe printing plate on a peripheral surface of the rotating drum arenipped between the chucks and the peripheral surface of the rotatingdrum.

Namely, a chuck which corresponds to one edge of the printing plate onthe peripheral surface of the rotating drum (e.g., a leading edgethereof in a direction it is wound) is attached in advance at apredetermined position on the rotating drum, and another chuck whichcorresponds to the other edge of the printing plate (e.g., a trailingedge thereof in a direction it is wound) is attached at a position onthe rotating drum in accordance with the size of the printing plateafter the printing plate has been wound onto the rotating drum.

The drum used in the above-described image exposure apparatus has aperipheral surface in a cylindrical shape. The printing plate is broughtinto tight contact with the peripheral surface of the drum in order todetermine a position of the printing plate in a thickness direction, sothat the printing plate can correspond to a depth of focus of a lightbeam for scan-exposure.

However, in the conventional drum, at least the peripheral surfacethereof needs to have an unfolded area which is larger than an area ofthe printing plate. Therefore, when a large-sized printing plate isused, a large-sized drum needs to be prepared. When the drum isenlarged, weight thereof is increased and rotation speed thereof isdecreased. In order to realize a high-speed processing, a high-powerdriving system is required to prevent the decrease of the rotationspeed.

SUMMARY OF THE INVENTION

In view of the above facts, an object of the present invention is toobtain a rotating body, whose weight is not increased even when it isenlarged so as to correspond to a large-sized sheet-type member, whichcan reliably wind and hold the sheet-type member thereon, and which canprevent a high-power driving system resulting from its increased weight.

In order to attain the above object, in accordance with an aspect of thepresent invention, there is provided a skeleton drum around which asheet can be wound and fixed, the drum comprising: (A) a rotating shaft;(B) a plurality of narrow cylindrical supports, each support having asupport surface for supporting the sheet and being arranged so as to becoaxial with the rotating shaft such that an interval, which is largerthan a width of the support, is formed between the supports; and (C) aplurality of chucks for pressing a leading edge and a trailing edge ofthe sheet toward the rotating shaft.

In accordance with another aspect of the present invention, there isprovided a skeleton drum around which a sheet can be wound and fixed,the drum comprising: (a) a rotating shaft; (B) a plurality of widecylindrical supports, each support having a support surface forsupporting the sheet and being arranged so as to be coaxial with therotating shaft such that an interval, which is smaller than a width ofthe each support, is formed between the supports; and (C) a plurality ofchucks for pressing a leading edge and a trailing edge of the sheettoward the rotating shaft.

In accordance with still another aspect of the present invention, thereis provided a skeleton drum, around which a sheet can be wound andfixed, and which has a substantial star-shape in sectional view, thedrum comprising: (a) a rotating shaft; (b) a plurality of plates, eachof the plates extending radially from an external periphery of therotating shaft, and having a support surface for supporting the sheet;and (c) a plurality of chucks for pressing a leading edge and a trailingedge of the sheet toward the rotating shaft.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic structural view showing an image exposureapparatus according to the present invention (corresponding to bothfirst and second embodiments).

FIG. 2 is a schematic structural view showing a recording portion of theimage exposure apparatus (corresponding to both first and secondembodiments).

FIG. 3 is a schematic perspective view of a rotating drum according tothe first embodiment.

FIG. 4 is a side view of a chuck according to the first embodiment.

FIG. 5 is a perspective view showing a schematic structure of therotating drum according to a modified example of the first embodiment.

FIG. 6 is a schematic perspective view of the rotating drum according tothe second embodiment.

FIG. 7 is a perspective view showing a schematic structure of therotating drum according to a modified example of the second embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

First Embodiment

Hereinafter, a preferred embodiment of the present invention will bedescribed with reference to drawings. FIG. 1 shows a schematic structureof an image exposure apparatus 10 according to a first embodiment. Theimage exposure apparatus 10 uses as a sheet-type member a photosensitiveplanographic printing plate 12 (hereinafter, referred to as a “printingplate”) comprising a photosensitive layer formed on a thin, rectangularplate-type support made of, for example, aluminum (for example, theprinting plate 12 has thickness dimension t of 0.3 mm and consistency cof 2.7×10³ kg/m³). The printing plate 12 is irradiated with a light beammodulated on the basis of image data, whereby the printing plate 12 isscan-exposed. The printing plate 12, for which image exposure has beencompleted by the image exposure apparatus 10, is then subjected todevelopment processing and the like by an unillustrated automaticdeveloping apparatus and the like. The minimum size of the printingplate 12 used in the first embodiment is 500×500×0.2 mm, and the maximumsize thereof is 1,160×940×0.3 mm.

A cassette loading section 18, a plate supplying/conveying section 20, arecording section 22 and a discharge buffer section 24 are providedinside a casing 14 of the image exposure apparatus 10. The cassetteloading section 18 is disposed at a lower-right side in the casing 14 asshown in FIG. 1. In the cassette loading section 18, a plurality ofcassettes 16, each accommodating a plurality of printing plates 12, isloaded in a state in which the cassettes 16 are inclined atpredetermined angle θ.

It is possible to process in the image exposure apparatus 10numerous-sized printing plates 12 having different longitudinal andtransverse dimensions. Printing plates 12 of whatever size areaccommodated in the cassettes 16 such that the photosensitive layers ofthe printing plates 12 face upward and an end thereof is positioned tocorrespond to a predetermined position. Further, a plurality of thecassettes 16 is loaded at predetermined intervals in the cassetteloading section 18 such that an end of the printing plates 12accommodated in each cassette 16 reaches a substantially constantheight.

The plate supplying/conveying section 20 is disposed above the cassetteloading section 18, and the recording section 22 is disposed at a lower,central area within of the apparatus, adjacent to the cassette loadingsection 18. The plate supplying/conveying section 20 is provided with apair of side panels 26 (in FIG. 1, only one side panel 26 is shown), andan inverting unit 28 and a feed unit 30 are mounted onto the side panels26.

The inverting unit 28 includes an inverting roller 32 having an externaldiameter of a predetermined dimension, and a plurality of small rollers(in the first embodiment, four small rollers 34A, 34B, 34C and 34D areshown as an example) is provided around the inverting roller 32. Thesmall rollers 34A through 34D are disposed so as to straddle the reverseroller 32 from the cassette loading section 18 to the recording section22, and an endless conveyor belt 36 is entrained between the smallrollers 34A to 34D. Accordingly, the conveyor belt 36 is wound on theinverting roller 32 so that the conveyor belt 36 is wound on roughlyhalf the circumference of the inverting roller 32 between the smallroller 34A and the small roller 34D.

The feed unit 30 includes a plurality of suction cups 38 that suck thetop end of the printing plate 12 inside the cassette 16. The suctioncups 38 are lowered to oppose the top end of the printing plate 12inside the cassette 16 loaded in the cassette loading section 18,whereby the printing plate 12 is sucked. The feed unit 30 then raisesthe suction cups 38 which have sucked the printing plate 12 whereby theprinting plate 12 is pulled out from the cassette 16 and a leading edgeof the pulled out printing plate 12 is inserted between the invertingroller 32 and the conveyor belt 36. In FIG. 1, movement positions of thesuction cups 38 are schematically shown with two-dot chain lines.

At the inverting unit 28, the inverting roller 32 and the conveyor belt36 rotate in the direction that the printing plate 12 is pulled out fromthe cassette 16 (direction of arrow A in FIG. 1). Accordingly, while theprinting plate 12 is being nipped between the inverting roller 32 andthe conveyor belt 36, the printing plate 12 is pulled out from thecassette 16 and wound onto the inverting roller 32. As a result, theprinting plate 12 is curved and conveyed such that the direction inwhich the printing plate 12 is conveyed is inverted. The radius of theinverting roller 32 is of a dimension (e.g., 100 mm or more) such thatkinks or bends are not generated in the printing plate 12 when theprinting plate 12 is curved.

As shown with solid lines and two-dot chain lines in FIG. 1, the sidepanels 26 horizontally move in accordance with the position of thecassette 16 from which the printing plate 12 is pulled out. Thus, thesuction cups 38 of the feed unit 30 oppose the printing plate 12 withinthe cassette 16 that has been selected.

Further, on the side panels 26, a guide 40 is provided below the smallroller 34D. The printing plate 12 which has been inverted by theinverting roller 32 is sent out from between the inverting roller 32 andthe conveyor belt 36 toward the guide 40 at the small roller 34D side. Aconveyor 42 is disposed above the recording section 22, and the printingplate 12 which has been sent out from the inverting unit 28 is guided tothe conveyor 42 by the guide 40.

When the side panels 26 move, the guide 40 swings so as to always orientthe direction in which the printing plate 12 is guided to the conveyor42. When the side panels 26 move, the small roller 34D at the recordingsection 22 side moves so as to change the direction in which theprinting plate 12 is sent out from the inverting unit 28, and when thesmall roller 34D moves, the small roller 34C moves so as to applysubstantially constant tension to the conveyor belt 36. As a result, theprinting plate 12 sent out from the inverting unit 28 is gently curvedby the guide 40.

In the conveyor 42, a conveyor belt 48 is entrained between a roller 44adjacent to an area below the plate supplying/conveying section 20 and aroller 46 adjacent to an area above the recording section 22. Theconveyor 42 is inclined so that the roller 46 is disposed lower than theroller 44.

As shown in FIGS. 1 and 2, in the conveyor 42, a roller 50 is disposedopposite to the roller 46. The printing plate 12 which has been sentonto the conveyor 42 is conveyed on the conveyor belt 48, and nippedbetween the rollers 46 and 50. In the recording section 22, a rotatingdrum 54 and a recording head portion 56 are mounted on a rack 52.Further, a puncher 58 is disposed above the rotating drum 54. Therotating drum 54 has radius r of 0.165 m.

As shown in FIG. 2, a gripper 60 is formed at the puncher 58. Theconveyor 42 nips the printing plate 12 between the rollers 46 and 50,and inserts the leading edge of the printing plate 12 into the gripper60 of the puncher 58 so as to hold it. When the leading edge of theprinting plate 12 has been inserted into the gripper 60, the puncher 58forms, for example, a notch for positioning, at a predetermined positionin the leading edge of the printing plate 12.

When the notch has been formed at the printing plate 12, the conveyor 42reversely drives the rollers 46 and 50 as well as the conveyor belt 48so as to pull out the leading edge of the printing plate 12 from thegripper 60 of the puncher 58. The conveyor 42 is provided with anunillustrated swinging apparatus, and lowered on an axis of the roller44 by the swinging apparatus such that the roller 46 approaches therotating drum 54 of the recording section 22 (this movement is shownwith two-dot chain lines in FIGS. 1 and 2). As a result, the leadingedge of the printing plate 12 on the conveyor belt 48 is oriented towarda predetermined position on an external peripheral surface of therotating drum 54, and the printing plate 12 is conveyed on the conveyorbelt 48 toward the rotating drum 54.

The rotating drum 54 is rotated by an unillustrated driving means in thedirection in which the printing plate 12 is attached to the rotatingdrum 54 and exposed thereon (i.e., the direction of arrow B in FIGS. 1and 2) and in the direction in which the printing plate 12 is detachedfrom the rotating drum 54 (i.e., the direction of arrow C in FIGS. 1 and2, which direction is opposite that of the direction in which theprinting plate 12 is attached to the rotating drum 54 and exposedthereon).

As shown in FIG. 2, a leading edge chuck 62 is attached at apredetermined position on the external peripheral surface of therotating drum 54 provided in the recording section 22. In the recordingsection 22, when the printing plate 12 is attached to the rotating drum54, the rotating drum 54 is initially stopped at a position where theleading edge chuck 62 opposes the leading edge of the printing plate 12sent by the conveyor 42 (i.e., the position at which the printing plate12 is attached to the rotating drum 54).

The recording section 22 is provided with an attachment cam 64 oppositeto the leading edge chuck 62 at the position at which the printing plate12 is attached to the rotating drum 54. When the attachment cam 64 isrotated, one end of the leading edge chuck 62 is pressed by theattachment cam 64. This enables the printing plate 12 to be insertedbetween the other end of the leading edge chuck 62 and the peripheralsurface of the rotating drum 54. In the recording section 22, in thisstate in which the leading edge of the printing plate 12 has beeninserted between the leading edge chuck 62 and the rotating drum 54, theattachment cam 64 is returned to the original position so as to bereleased from pressing the leading edge chuck 62, whereby the leadingedge of the printing plate 12 can be nipped and held between the leadingedge chuck 62 and the peripheral surface of the rotating drum 54. Atthis time, an unillustrated positioning pin protruding at apredetermined position on the peripheral surface of the rotating drum 54is inserted into the notch formed by the puncher 58 to position theprinting plate 12 on the rotating drum 54.

In the recording section 22, when the leading edge of the printing plate12 is fixed on the rotating drum 54, the rotating drum 54 is rotated inthe direction in which the printing plate 12 is attached to the rotatingdrum 54 and exposed thereon. Accordingly, the printing plate 12 sentfrom the conveyor 42 is wound on the peripheral surface of the rotatingdrum 54.

A squeeze roller 66 is disposed near the peripheral surface of therotating drum 54 and further downstream, in the direction in which theprinting plate 12 is attached to the rotating drum 54 and exposedthereon, than the position at which the printing plate 12 is attached tothe rotating drum 54. The squeeze roller 66 moves toward the rotatingdrum 54, and presses the printing plate 12 wound onto the rotating drum54 toward the rotating drum 54 so as to bring the printing plate 12 intoclose contact with the peripheral surface of the rotating drum 54.

Further, a trailing edge chuck attachment/detachment unit 68 is disposednear a further upstream side than the squeeze roller 66 in the directionin which the printing plate 12 is attached to the rotating drum 54 andexposed thereon. A detachment cam 70 is disposed near a furtherdownstream side than the squeeze roller 66 in the direction in which theprinting plate 12 is attached to the rotating drum 54 and exposedthereon. In the trailing edge chuck attachment/detachment unit 68, atrailing edge chuck 74 is attached to a distal end of a shaft 72 thatprotrudes toward the rotating drum 54.

The printing plate 12 is positioned by an unillustrated mechanism suchthat the trailing edge chuck attachment/detachment unit 68 opposes thetrailing edge of the printing plate 12 that is wound around the rotatingdrum 54. When the trailing edge chuck attachment/detachment unit 68 hasopposed the trailing edge of the printing plate 12, the shaft 72 isprotruded so that the trailing edge chuck 74 is attached and fixed atthe predetermined position on the rotating drum 54. As a result, thetrailing edge of the printing plate 12 is nipped and held between thetrailing edge chuck 74 and the rotating drum 54.

When the leading edge and the trailing edge of the printing plate 12have been held on the rotating drum 54, the squeeze roller 66 isseparated therefrom. Then, in the recording section 22, while therotating drum 54 is rapidly rotated at a predetermined rotational speed,the printing plate 12 is irradiated with a light beam modulated on thebasis of image data emitted from the recording head portion 56synchronously with the rotation of the rotating drum 54. In this way,the printing plate 12 is scan-exposed on the basis of the image data.

After scan-exposure of the printing plate 12 has been completed, therotation of the rotating drum 54 is stopped when the trailing edge chuck74 holding the trailing edge of the printing plate 12 positions oppositeto the trailing edge chuck attachment/detachment unit 68. The squeezeroller 66 moves toward the rotating drum 54 to press the printing plate12. After that, the trailing edge chuck attachment/detachment unit 68receives the trailing edge chuck 74, and separates the trailing edgechuck 74 from the rotating drum 54. As a result, the trailing edge ofthe printing plate 12 is completely released.

After the trailing edge chuck 74 has been detached from the rotatingdrum 54, the rotating drum 54 is rotated in the direction in which theprinting plate 12 is detached therefrom. Accordingly, the printing plate12 is sent out from between the squeeze roller 66 and the rotating drum54.

In the same manner as the leading edge chuck 62, the trailing edge chuck74 may be an opening/closing type fixed in advance on the rotating drum54 instead of the attachment/detachment type.

As shown in FIG. 1, the discharge buffer section 24 is provided abovethe squeeze roller 66. When the rotating drum 54 is rotated in thedirection in which the printing plate 12 is detached therefrom, thetrailing edge of the printing plate 12 is sent out toward the dischargebuffer section 24. Further, when the rotating drum 54 is rotated in thedirection in which the printing plate 12 is detached therefrom (in thedirection of arrow C), if the leading edge chuck 62 has reached theposition at which the printing plate 12 is detached from the rotatingdrum 54, which position is opposite to the detachment cam 70, therotating drum 54 is stopped. In the recording section 22, the detachmentcam 70 is rotated at this position so as to press the leading edge chuck62, and the leading edge of the printing plate 12 is released from beingnipped between the leading edge chuck 62 and the rotating drum 54. As aresult, the printing plate 12 is detached from the rotating drum 54.

The discharge buffer section 24 includes a discharge roller 78, which isprovided at an inner side of a discharge port 76 formed at the casing14. A plurality of small rollers (small rollers 80A, 80B, 80C, 80D and80E are shown as an example) are disposed around the discharge roller78, and an endless conveyor belt 82 is entrained between the smallrollers 80A to 80E. The conveyor belt 82 is thus entrained between thesmall rollers 80A through 80E around the discharge roller 78 in a rangeof between ½ to ¾ the circumference of the discharge roller 78.

The small roller 80A protrudes toward the squeeze roller 66 side of therecording section 22, and a roller 84 is disposed opposite to the smallroller 80A. The printing plate 12 which has been sent out from therecording section 22 is guided toward between the small roller 80A andthe roller 84 to be nipped therebetween.

In the discharge buffer section 24, when the discharge roller 78 isrotatably driven in a direction in which the printing plate 12 is pulledin (direction of arrow D), the printing plate 12 which has been nippedbetween the small roller 80A and the roller 84 is pulled out from therecording section 22 and guided to between the discharge roller 78 andthe conveyor belt 82. Then, the printing plate 12 is nipped between thedischarge roller 78 and the conveyor belt 82, and wound around thedischarge roller 78. At this time, in the discharge buffer section 24,the leading edge portion of the printing plate 12 (the trailing edgeside thereof in the direction in which it is sent out from the recordingsection 22) is nipped between the small roller 80A and the roller 84,whereby the printing plate 12 which has been wound onto the dischargeroller 78 is temporarily held.

As shown with two-dot chain lines in FIG. 1, in the discharge buffersection 24, the small roller 80A and the roller 84 move to a positionwhich faces the discharge port 76. At this time, the small roller 80Aand the idle roller 84 move integrally such that the leading edge of theprinting plate 12 is oriented toward the discharge port 76. The smallroller 80B, which is above the small roller 80A, moves in accordancewith the movement of small roller 80B so as to apply constant tension tothe conveyor belt 82.

In the discharge buffer section 24, when the leading edge of theprinting plate 12 has been oriented to the discharge port 76, thedischarge roller 78 is rotatably driven in the direction in which theprinting plate 12 is sent out (direction which is opposite to arrow D)at a rotational speed in accordance with the speed at which the printingplate 12 is conveyed by processing apparatuses, such as an automaticdevelopment apparatus, disposed adjacent to the discharge port 76.Accordingly, the printing plate 12 is sent out from the discharge port76.

FIG. 3 shows a structure of the rotating drum 54 in detail.

Both ends of a rotating shaft 200 are pivotally supported byunillustrated bearings, and a connecting member (e.g., a gear or asprocket) of a driving system is attached to one end of the rotatingshaft 200. Thus, when the connecting member receives rotation force of adriving portion, the rotating shaft 200 can rotate.

A length of the rotating shaft 200 in an axial direction is set to belarger than the maximum width of the printing plate 12.

Wheel-shaped guide members 204 are attached to the rotating shaft 200 inthe axial direction at predetermined intervals.

In the guide member 204, ribs 208 having short widths extend radiallyfrom a bearing 206 into which the rotating shaft 200 is inserted andfitted. The ribs 208 have thin-plate shapes, and longitudinal dimensionsthereof are substantially identical to each other.

Outer ends of the ribs 208 are fixed to an inner peripheral surface ofcylinders 210. Namely, the rotating shaft 200 supports the cylinders 210with the ribs 208. A width of the cylinder 210 is substantiallyidentical to that of the ribs 208.

The guide member 204 is composed of the ribs 208 and the cylinder 210.An outer periphery of the cylinder 210 is located around acircumferential locus of predetermined radius of the rotating shaft 200,and serves as a surface onto which the printing plate 12 is wound.

In the first embodiment, multiple (five) guide members 204 are disposedalong the axis of the rotating shaft 200.

Thus, along the axis of the rotating shaft 200, only areas of theprinting plate 12 corresponding to the cylindrical bodies 210 aresupported, and the other areas are suspended between the cylindricalbodies 210. In the first embodiment, a ratio of the supported width ofthe printing plate 12 to the entire width thereof, in consideration ofthe material and the thickness of the printing plate 12, is ⅕.

Chuck holders 212 are provided at the rotating shaft 200 between theguide members 204. The chuck holders 212 comprise a base 214, which isdisposed around a peripheral surface of the rotating shaft 200, and apair of arms 216 that extend radially, relative to the rotating shaft200, from both longitudinal ends of the base 214 and are parallel toeach other.

The rotating shaft 200 is inserted through rings 218 which are providedat both longitudinal ends of the base 214, and the chuck holder 212 isthereby supported so that it can rotate relative to the rotating shaft200.

An attachment/detachment portion 220 (see FIG. 4) for the trailing edgechuck 74, which is a fixing means, is formed at a distal end of the arms216 of the chuck holders 212 so that the trailing edge chuck 74 can beattached to and detached from the chuck holder 212. Further, a cylinder222, onto which the base 214 is fixed, is provided between the rings 218of the chuck holders 212.

The cylinder 222 is pivotally supported by the rotating shaft 200, andconstant force springs 224 are attached to portions of an outerperiphery of the cylinder 222. Although a detailed description will beomitted, the constant force springs 224 serve to urge the chuck holders212 in a direction which makes the printing plate 12 taut, in a state inwhich the printing plate 12 is held by the trailing edge chucks 74 thathave been attached to the attachment/detachment portions 220.

The trailing edge chucks 74 are formed by the four plates 150 whoselengths correspond to the intervals between the guide members 204. Asshown in FIG. 4, the plate 150 is structured so as to pivot like aseesaw in a width direction of the plate 150 with a post 154 as afulcrum. The post 154 attaches to and detaches from the chuck holdingbody 212.

As shown in FIG. 4, in a state in which all parts have been attached tothe plates 150, a center of gravity 155 of the plate 150 is positionedfurther to a right side of FIG. 4 than an axis of the post 154.

A clamp 160 is formed at one end of the plate 150 in the width directionthereof (a left end in FIG. 4). The clamp 160 is formed so as to bendsubstantially perpendicular to the plate 150 toward the rotating shaft200, and a rubber sheet 161 is stuck on an end surface of the clamp 160.The rubber sheet 161 is a portion in direct contact with the printingplate 12, and is an important element which determines a coefficient offriction when the printing plate 12 is nipped between the clamp 160 andthe peripheral surface of the cylindrical body 210. Namely, acoefficient of friction μ1 between the clamp 160 and the printing plate12 is determined by the rubber sheet 161. A coefficient of friction μ2between the printing plate 12 and the outer periphery of the cylindricalbody 210 is determined by material of each or the equivalent.

Further, one end of a plate spring 180 which is bent in a substantiallyL-shape is fixed on a lower surface of a right end of the plate 150shown in FIG. 4. The plate spring 180 is bent toward the rotating drum54, and an anchor 182 is attached to the other end of the plate spring180. A surface of a tip of the anchor 182 is formed in an arced shape.

The plate spring 180 contacts and engages with the attachment/detachmentportion 220 via the anchor 182. When the trailing edge chuck 74approaches the chuck holding body 212, initially, the anchor 182 comesinto contact with the attachment/detachment portion 220. Then, as thetrailing edge chuck 74 continues to approach the chuck holders 212, theplate spring 180 is elastically deformed. Urging force generated by theelastic deformation of the plate spring 180 pivots the plate 150 on thepost 154, and clamping force is thereby generated by the clamp 160.

The leading edge chuck 62, which has substantially the same structure asthat of the trailing edge chuck 74, is attached to the guide members 204at a predetermined position so as to wait for and clamp the leading edgeof the printing plate 12 approaching from a tangential direction of therotating drum 54. Since the printing plates 12 have various lengthdimensions depending on their size, the locations of the trailing edgesafter the printing plates 12 are wrapped are different. Accordingly, therotating drum 54 of the present invention has a structure in which aposition of the chuck holder 212 around the rotating shaft 200 isdetermined in accordance with the length of the printing plate 12 andthe trailing edge chuck 74 is attached to the chuck holding body 212with a predetermined timing so as to clamp the trailing edge of theprinting plate 12. As a result, the leading edge and the trailing edgeof the printing plate 12 can be clamped.

Hereinafter, an operation of the first embodiment will be described.

In the image exposure apparatus 10, when image data to be exposed ontothe printing plate 12 is input, the size and the number of printingplates 12 to be subjected to image exposure are set, and when the imageexposure is instructed to initiate, image exposure processing for theprinting plates 12 initiates. The order to initiate the image exposureprocess may be given by operating an operation panel switch disposed theimage exposure apparatus 10, or may be given by signals from an imagingapparatus or the like which outputs image data to the image exposureapparatus 10.

In the image exposure apparatus 10, when the image exposure processingis instructed to initiate, the feed unit 30 and the inverting unit 28are moved to a position which corresponds to the cassette 16accommodating the printing plates 12 having a specified size, theprinting plate 12 in the cassette 16 is sucked and pulled out by thesuction cups 38, and the printing plate 12 is fed between the invertingroller 32 of the inverting unit 28 and the conveyor belt 36.Accordingly, the printing plate 12 is nipped between the invertingroller 32 and the conveyor belt 36, and conveyed to the conveyor 42.

First, the conveyor 42 inserts the leading edge of the printing plate 12into the gripper 60 of the puncher 58. Then, the puncher 58 forms thenotch for positioning, at a predetermined position in the insertedprinting plate 12. When the notch has been formed at the printing plate12, the conveyor 42 pulls the printing plate 12 out from the gripper 60of the puncher 58, and feeds out the printing plate 12 toward theperipheral surface of the rotating drum 54.

In the recording section 22, when the leading edge of the printing plate12 is held against the rotating drum 54 by the leading edge chuck 62,the printing plate 12 is wound onto the rotating drum 54 while beingsqueezed by the squeeze roller 66, and the trailing edge of the printingplate 12 is held against the rotating drum 54 by the trailing edge chuck74.

Thereafter, in the recording section 22, while the rotating drum 54 isbeing rapidly rotated, the printing plate 12 is irradiated, on the basisof image data, with a light beam emitted from the recording head portion56 to scan-expose the printing plate 12. While the rotating drum 54 isbeing rapidly rotated, a force for nipping the printing plate 12 isapplied to the leading edge chuck 62 and the trailing edge chuck 74 by acentrifugal force generated by the rotation of the rotating drum 54.

When the scan-exposure for the printing plate 12 has been completed, theleading edge chuck 62 is removed, and the printing plate 12 is fed outto the discharge buffer section 24.

In the discharge buffer section 24, the printing plate 12 is nippedbetween and conveyed by the small roller 80A and the roller 84 so as tobe wound onto the discharge roller 78. After that, the small roller 80Aand the roller 84 are moved opposite to the discharge port 76, and theprinting plate 12 is fed out from the discharge port 76 at apredetermined conveyance speed.

Next, a procedure for nipping and tensing the printing plate 12 betweenthe rotating drum 54 and the leading edge chuck 62 or the trailing edgechuck 74, and maintenance of this state will be described.

When the leading edge of the printing plate 12 is inserted between thecylindrical bodies 210 of the guide members 204 and the plates 150, theleading edge chuck 62 is released from being prevented from rotating bythe cam 64, such that the plates 150 pivot on the posts 154 due tourging force of the plate springs 180. This pivot moves the clampportions 160 toward the peripheral surface of the rotating drum 54 sothat the printing plate 12 can be nipped between the clamp portions 160and the outer peripheries of the cylinders 210.

Further, the trailing edge chuck 74 is attached to the rotating drum 54when the printing plate 12 has reached a predetermined position.Therefore, while the trailing edge chuck 74 is moving to be attachedthereto, the plates 150 gradually pivot on the posts 154 due to urgingforce of the plate springs 180 so that the printing plate 12 which hasbeen positioned can be nipped between the clamps 160 and the outersurfaces of the cylinders 210 of the guide members 204.

When the printing plate 12 has been completely chucked by the leadingedge chuck 62 and the trailing edge chuck 74, the rotating drum 54starts to rotate rapidly for image recording.

Since the center of gravity 155 of the plate 150 is positioned at theside of the post 154 opposite to the clamp 160, centrifugal force isapplied to the center of gravity 155 in the same direction as thedirection in which the plate spring 180 urges. Accordingly, while therotating drum 54 is being rapidly rotated, namely, while images arebeing recorded, the force for nipping the printing plate 12 can beincreased.

The external surface of the rotating drum 54 in the first embodiment issubstantially composed of only the outer surfaces of the cylinders 210of the guide members 204. Namely, the total area of the outer peripheralsurfaces of the cylindrical bodies 210 is one fifth of the area of theexternal peripheral surface of the rotating drum 54.

The printing plate 12 is only engaged and guided by the outer surfacesof the cylinders 210 so as to be wound and supported thereon. Thecylinder 210 is coaxially supported by the plural ribs 208 around therotating shaft 200 so as to not become eccentric.

Five cylinders 210 are disposed along the axis of the rotating shaft 200at predetermined intervals. Therefore, the cylinders 210 can support theentire printing plate 12 with substantially equal balance.

Further, the total area of the peripheral surfaces of the cylinders 210can be determined based on a material and a thickness of the sheet-typemember (the printing plate 12 in the first embodiment) to be wound.Since the printing plate 12 comprises the photosensitive layer formed(applied) on the support made of metal (aluminum) so as to have a degreeof firmness, the printing plate 12 can hold itself in a substantiallycylindrical shape even if it is merely rolled in the air. Therefore, theprinting plate 12 can be accurately wound and held on the peripherallocus of a predetermined radius coaxial with the rotating shaft 200merely by partially disposing the guide members 204 as auxiliary guidesfor the printing plate 12 to be positioned and winded upon.

In this case, each cylinder 210 has a continuous outer surfaceconcentric with the rotating shaft 200, and thus, the locus around whichthe printing plate 12 is wound can be always maintained.

Accordingly, weight of the rotating drum 54 itself can be significantlyreduced. As a result, the rapid rotation of the rotating drum 54required for high-speed processing can be realized by a low-powerdriving system. Namely, an expensive high-power driving system is notnecessary.

In the first embodiment, the total area of the outer surfaces of thecylindrical bodies 210 of the guide members 204 is about one fifth ofthe area of the peripheral surface of the entire rotating drum 54.However, when a non-firm sheet-type member (printing plate 12) is woundthereon, a width of the cylinder 210 may be increased as shown in FIG.5. In this case, a width of the rib 208 connecting the rotating shaft200 and the cylinder 210 is also preferably increased.

In this case, if the adjacent guide members 204 contact each other, therotating drum 54 having such guide members 204 is substantially the sameas a conventional rotating drum 54, and is merely structured by separateparts. However, the object of the present invention is to lighten therotating drum 54 as much as possible by reducing the area of theperipheral surface of the rotating drum 54 which contacts the woundprinting plate 12. As a result (as a structure producing the fewestresults), even if the gap between the guide members 204 is slight (asshown in FIG. 5), the rotating drum 54 which is intended to be lightenedis different from that whose entire peripheral surface is justseparately formed from the first, in their ideas.

Second Embodiment

Hereinafter, a second embodiment of the present invention will bedescribed. In the following description of the second embodiment,components identical to those in the first embodiment will be referredto using the same reference numerals, and description thereof will beomitted. Namely, since the rotating drum 54 shown in FIG. 6 is a featureof the second embodiment, the overall structure of the device is thesame as that shown in FIGS. 1 and 2 used for the first embodiment, anddescription thereof will be omitted.

As shown in FIG. 6, in the rotating drum 54 of the second embodiment,six elongated plates 228 which have sides 226 continuing along the axisof the rotating shaft 200 are provided around the rotating shaft 200 atintervals of a predetermined angle. Namely, in a sectional view which isperpendicular to the rotating shaft 200, the rotating drum 54 isstar-shaped.

The plates 228 extend radially from the rotating shaft 200, with thesides 226 forming bases (proximal ends of the plates 228). Distal endsof the plates 228 are disposed on the peripheral locus for winding theprinting plate 12.

The leading edge chuck 62 is attached to the distal end of only one ofthe six plates 228. The leading edge chuck 62 is substantially the sameas that shown in FIG. 3. Similarly, the trailing edge chuck 74 issubstantially the same as that shown in FIG. 3. However, since FIG. 6shows a state in which the trailing edge chuck 74 is detached from theattachment/detachment portion 220, the trailing edge chuck 74 is notillustrated.

In the second embodiment, the distal ends of the plates 228 continuealong the axial direction of the rotating shaft 200. This isparticularly advantageous to hold the leading edge and the trailing edgeof the printing plate 12 with the leading edge chuck 62 and the trailingedge chuck 74.

The printing plate 12 is intermittently supported around the rotatingshaft 200. However, since the printing plate 12 used in the secondembodiment is thick and made of a firm material, the printing plate 12is suspended between the plates 228 with an arc having a uniform radiusof curvature so that a satisfactorily cylindrical locus (peripherallocus) can be obtained, merely by being intermittently supported in thedirection it is wound.

When the sufficiently cylindrical locus cannot be obtained by changingthe material or the like, a cylindrical bridging member 230 may besuspended between the plates 228 and attached as shown in FIG. 7. Thebridging member 230 itself need not have a high strength, and can be athin, film-type member.

Finally, a case in which centrifugal force is used in order to increasethe holding force of the chucks while the printing plate 12 is beingnipped and held by the leading edge chuck 62 and the trailing edge chuck74 of the first and second embodiments will be described.

In this case, since the centrifugal force generated when the rotatingdrum 54 rotates rapidly is added to the spring force of the platesprings 180, the force of the leading edge chuck 62 and the trailingedge chuck 74 for holding the printing plate 12 is increased.

The leading edge chuck 62 and the trailing edge chuck 74 are structuredso as to have dimensions, for example, shown in the following table 1.In table 1, thickness dimension t and consistency c of the printingplate 12, radius r of the rotating drum 54, and coefficients of frictionμ1 and μ2 are also listed.

TABLE 1 Items Symbols Values Weight of Chuck m 0.251 kg (Width of Chuck:300 mm) Distance from L1  30 × 10⁻³ m Post Centerline to Clamp Distancefrom Post Centerline to —  20 × 10⁻³ m Non-clamp End Distance from PostCenterline to L2 6.9 × 10⁻³ m Center of Gravity Coefficient of Frictionbetween μ1 1.0 Clamp Portion and Printing Plate Coefficient of Frictionbetween μ2 0.5 Printing Plate and Peripheral Surface of Cylindrical BodyRadius of Rotating Drum r 0.165 Density of Printing Plate c 2.7 × 10³kg/m Thickness of t 0.3 × 10⁻³ m Printing Plate

These values listed in table 1 are set so that the following formula (1)can be formed and a maximum holding force due to the centrifugal forcecan be achieved.

{(μ1+μ2)×(L1/L2)×m}>c×r×t  (1)

As described above, in accordance with the present invention, even whenthe drum is enlarged so as to correspond to a large-sized sheet-typemember, weight of the drum is not significantly increased, and the drumcan reliably wind and hold the sheet-type member. Further, the drum ofthe present invention can avoid the need for a high-power driving systemfor the increased weight.

What is claimed is:
 1. A skeleton drum around which a sheet can be woundand fixed, the drum comprising: (A) a rotating shaft; (B) a plurality ofnarrow cylindrical supports, each support having a support surface forsupporting the sheet and being arranged so as to be coaxial with therotating shaft such that an interval, which is larger than a width ofthe support, is formed between the supports; and (C) a plurality ofchucks for pressing a leading edge and a trailing edge of the sheettoward the rotating shaft.
 2. The drum of claim 1, wherein the drum isfor fixing the sheet when the sheet is to be scan-exposed.
 3. The drumof claim 1, wherein each of the supports comprises a bearing attachedaround the rotating shaft, a narrow cylinder coaxial with the rotatingshaft, and a plurality of ribs integrally connecting the bearing and thenarrow cylinder.
 4. The drum of claim 1, wherein the support surface ofeach support exists on an imaginary cylindrical surface which is coaxialwith the rotating shaft.
 5. The drum of claim 1, wherein the supportsurface of each support extends around a periphery of the drum.
 6. Thedrum of claim 1, wherein the chucks include a leading edge chuck forpressing the leading edge of the sheet, and a trailing edge chuck forpressing the trailing edge of the sheet.
 7. The drum of claim 6, whereina position of the leading edge chuck around the periphery of the drum isfixed, and a position of the trailing edge chuck around the periphery ofthe drum is changeable.
 8. The drum of claim 6, further comprising anurging structure, which urges the trailing edge chuck to pull the sheetaround the periphery of the drum when the sheet is pressed by thetrailing edge chuck.
 9. The drum of claim 6, wherein the trailing edgechuck comprises: a support structure comprising a support that isremovably attached to the drum; a plate, one end of which is forpressing the trailing edge of the sheet, and which is pivotallyconnected to the drum via the support structure; and an elastic elementconnected to an other end of the plate which, when the support isattached to the drum, applies force to the other end of the plate bybeing elastically deformed such that the one end of the plate pivotallyrotates toward the rotating shaft to press the sheet.
 10. The drum ofclaim 9, wherein a center of gravity of the plate is positioned betweenthe ends, and the support is connected to the plate on the side of theone end, relative to the center of gravity such that a centrifugal forceacting on the plate when the drum is rotated increases force forpressing the sheet.